Constant current circuit

ABSTRACT

The circuit is designed to produce a substantially constant current from a source of voltage which is subject to variations and includes first and second transistors of opposite conductivity types, the base of each transistor being connected to the collector electrode of the opposite transistor and the emitter electrodes of the two transistors being connected to opposite terminals of a voltage source, a pair of diode means separately connected in parallel between the emitter and base electrodes of each of the first and second transistors, respectively, and a third transistor whose base and emitter electrodes are connected in parallel between the base and emitter electrodes of the first or second transistor, whereby the collector current of the third transistor is utilized as a constant current source which is not subject to changes because of fluctuations of the source voltage.

United States Patent Ohsawa 1 Aug. 19, 1975 l l CONSTANT CURRENT CIRCUIT Pri'lriur'y 111m!uilierGerald Goldberg Inventor: Mitsuo Ohsawa. Fujisuwa Japan Attorney, Again. or FirmLewis H. Eslinger; Alvin Smderbrand [73] Assignee: Sony Corporation Tokyo Japan [22 Filed: June I. 1973 [2|] Appl. No.1 365,849 [57] ABSTRACT [30] Foreign Apphcauon priority Data The circuit is designed to produce a substantially conjunc (L Jupu" 4756349 stant current from a source of voltage which is subject ju'lc 1973 Jilplm 47-5535 to variations and includes first and second transistors of opposite conductivity types. the base of each tranl l Cl 323/4; 333/49? 323/22 T1 sistor being connected to the collector electrode of 307/2973 330/20 the Opposite transistor and the emitter electrodes of l5 ll GOSF U56; HO3F 3/213 the two transistors being Connected to opposite termil58l Field M Search 323/] 22 T3 nals of a voltage source. a pair of diode means scpa Run/2973 33olzu- 38 M ratel connected in parallel between the emitter and base electrodes of each of the first and second transisl References Cited tors, respectively, and a third transistor whose base UNITED STATES PATENT and emitter electrodes are connected in parallel be- 3 392,344 7/1968 Meacham 4. 323/4 tween the base and emitter electrodes of the first or 3,523,521 8/1970 Lloyd 323M second transistor, whereby the collector current of the 3555.30 H1 71 Lim erg-i... /4 third transistor is utiliyed as a constant current source 3t l7. ll/l D hkin l l 333/4 which is not subject to changes because of fluctuations 3.64Kl53 3/l97: Graf 323/] f the Suurcc \Uhagc' 165L347 3/l972 Limberguu. 323/! X 3.777.25l l1/l973 Cecil ct ail 323/4 OTHER PUBLICATIONS Two-'lerminal ConstantCurrent Device by F C.

Allen. EEE 0m. 1965 pp. 71. 72.

3 Claims. ll Drawing Figures ne e l CONSTANT CURRENT CIRCUIT BACKGROUND OF THE INVENTION The present invention relates to a constant current circuit and more particularly to a constant current circuit which is subject to a minimum of influence due to variations in the source voltage and which is suitable for manufacture in integrated circuit form.

Various types of constant current transistorized circuits are known and two of these are shown in FIGS. 1 and 2. In the circuit of FIG. I the collector current I flowing from the transistor I and in the circuit of FIG. 2 the current I,- flowing into the transistor I are made constant. In both of these circuits the transistor 1 is supplied at its base electrode with a constant voltage determined by a diode 2 so that the collector current of the transistor I is kept substantially constant provided the source voltage V is constant. In all of the embodiments to be discussed in this application it is assumed that a load. through which the collector current I,- flows. is connected between the appropriate transistor lead and either the circuit ground of the source voltage.

The prior art constant current circuits depicted in FIGS. I and 2 have the disadvantage that when the supply voltage V is varied. the forward current in the diode 2 is varied so as to change the forward bias volt age supplied to the transistor 1 with the result that the collector current I, is also changed. Furthermore in these constant current circuits. when the supply voltage V includes ripple components. the output current of the described circuit is again varied in response to the ripple components. Therefore such circuits have the defect that their operations are unstable and their signal to noise ratios are deteriorated.

SUMMARY OF THE INVENTION The above and other disadvantages are overcome by the present invention of a constant current circuit comprising a voltage source having at least two terminals. first and second semiconductor devices each having base. emitter and collector electrodes. the base electrode of each semiconductor device being connected to the collector electrode of the other semiconductor device, the respective emitter electrodes of the first and second semiconductor device being connected to separate terminals of the voltage source. third and fourth semiconductor means for providing a biasing voltage to the base and emitter of each of the first and second semiconductor devices. and a fifth semiconductor device having base. emitter and collector electrodes. the base and emitter electrodes of the fifth semiconductor device being connected to the base and emitter electrodes of at least one of the first and second semiconductor devices. so that the collector current of the fifth semiconductor device is utilizable as a constant current source.

In one preferred embodiment the first and fifth semiconductors are transistors of one conductivity type and the second semiconductor is a transistor of an opposite conductivity type. The third and fourth semiconductor means are either diodes or transistors connected in a diode configuration. In still another embodiment a sixth semiconductor device having base. emitter and collector electrodes is provided and is connected such that the base and emitter electrodes of the sixth semiconductor device are connected to the base and emitter electrodes. respectively, of the other of the first and second semiconductor devices so that the collector currents of both the fifth and sixth transistors are utilizable as a constant current source.

This second embodiment may be further modified by adding means for providing a constant voltage which is connected between the collector electrodes of the fifth and sixth transistors and a load connected in parallel with the constant voltage means. In one such embodiment the constant voltage means comprises a loner diode.

In still other embodiments the constant current circuit according to the invention is utilized in an integrated circuit. direct coupled transistor amplifier.

It is therefore a principle object of the present invention to provide a constant current circuit in which a constant current is obtained despite variations in the source voltage.

It is another object of the invention to provide a constant current circuit suitable for manufacture as an integrated circuit.

It is a further object of the invention to provide a constant current circuit which is suitable for use in an integrated circuit amplifier.

It is still a further object of the invention to provide a constant current circuit suitable for use in a constant voltage circuit.

The foregoing and other objectives, features. and advantages of the invention will be more readily understood upon consideration of the following detailed description of certain preferred embodiments of the invention. taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. I and 2 are schematic diagrams illustrating prior art constant current circuits;

FIG. 3 is a schematic diagram of a constant current circuit according to one embodiment of the invention;

FIG. 4 is a schematic diagram of a constant current circuit of the embodiment of FIG. 3 when adapted to be used with an integrated circuit amplifier;

FIG. 5 is a schematic diagram of a second embodiment of a constant current circuit according to the invention;

FIG. 6 is a diagram comparing the supply voltage versus output current characteristic curves of the constant current circuits of the embodiments of FIGS. I and 5;

FIG. 7 is a schematic diagram of an integrated circuit amplifier utilizing a constant current circuit according to the embodiment of FIG. 5;

FIG. 8 is a schematic diagram of a constant voltage source of the non-grounded type utilizing a constant current circuit according to the embodiment of FIG. 3'.

FIGS. 9 and I0 are schematic diagrams used for explaining the operation of the constant voltage source in FIG. 8; and

FIG. 11 is a schematic diagram of a second embodiment of a constant voltage source of thc nongrounded type utilizing the constant current circuit of the embodiment of FIG. 5.

DESCRIPTION OF CERTAIN PREFERRED EMBODIMENTS Referring now more particularly to FIG. 3 one embodiment of a constant current circuit according to the invention which is formed on a single monolithic IC' chip is illustrated. The base and collector electrodes of a PNP transistor 3 are respectively connected to the collector and base electrodes of an NPN transistor 4, while the emitter electrode of the transistor 3 is connected to the plus terminal 11 of an external voltage source and the emitter electrode of the transistor 4 is connected to the other terminal 12 of the voltage source V... which is also the circuit ground. The collector and base electrodes of an NPN transistor are connected to the emitter electrode of the transistor 3. The emitter electrode of the transistor 5 is connected to the base electrode of the transistor 3. Thus the transistor 5 is connected in a diode configuration. Similarly. a diode-connected NPN transistor 6 has its base and col lector electrodes connected to the base of the transistor 4 and its emitter electrode connected to the emitter electrode of the transistor 4. A PNP transistor 7 is connected with its emitter and base electrodes to the emitter and base electrodes of the transistor 3, respectively. An NPN transistor 8 is similarly connected with its base and emitter electrodes to the base and emitter elec trodes of the transistor 4. respectively.

With such an arrangement the voltage appearing between the base and emitter electrodes of the transistor 5 is applied as a bias voltage to the bases of the transistors 3 and 7. Similarly the voltage obtained between the base and emitter electrodes of the transistor 6 is supplied as a base bias voltage to the transistors 4 and 8.

In operation. when the supply voltage V is applied to the above-described circuit a collector current I flows through the transistor 3 initially. This develops a forward voltage between the base and emitter of the transistor 6 to cause a collector current I to flow through the transistor 4 due to the forward base bias voltage from the transistor 6. The flow of the collector current I, through the transistor 4 develops a forward voltage between the base and emitter electrodes of the transistor 5 which thereby forward biases the transistor 3 to sustain the current 1 if the transistors 5 and 6 are silicon transistors then the base bias voltages produced by the currents flowing through them are substantially constant at 0.6 volts. This means that the base bias voltage to the transistors 3 and 4 are substantially the same and thus their collector currents are substantially the same if the transistors 3 and 4 are made adjacent to each other on the same IC chi so as to have substantially the same operating characteristics. Furthermore the base and collector electrodes of the transistors 3 and 4 form a positive feedback loop so that the collector currents and I are mutually sustaining for each other. That is. if the collector current I is constant the voltage between the base and emitter of the transistor 6 is constant which thereby makes the collector current I constant and this current flowing through the transistor 5 ensures that the transistor 3 is biased to keep the collector current I, also constant.

Since the collector currents i and I may be made equal and constant. the base biasing voltages applied to the transistors 7 and 8 are also the same and constant. In general. the collector current of a transistor with respect to a predetermined base biasing voltage can be made to have a particular value by the suitable selection of the base diffusion area of the transistor. Thus the base diffusion areas of the transistors 7 and 8 are suitably selected to cause the currents L and l,-,. to flow from or to the respective collector electrodes with a predetermined magnitude when appropriate loads are connected between the collector and the transistor 7 and the circuit ground and the collector of the transistor 8 and the positive terminal ll of the voltage source in the above-described circuit. when the supply voltage V,.,. is varied, the voltage between the collector and emitter electrodes of the transistor 3 is increased and decreased in accordance with the variation of the supply voltage because the voltage between the base and the emitter electrodes of the diode connected transistor 6 is substantially constant at 0.6 volts. The collector current I of the transistor nevertheless remains substantially constant with respect to the variation of the voltage between the collector and emitter electrodes of the transistor 3 because of the well known output characteristic. that is the I versus V characteristic (not shown) of silicon transistors. This characteristic is such that current I when in saturation. remains substantially constant despite increases in the V provided a constant base current is supplied. Accordingly. the collector currents of the transistors 7 and 8 are kept constant by supplying the constant base bias voltage and the constant base current.

Several advantages are obtained with this embodiment. In the first place, since variations in the voltage source V have no effect on the constant current outputs from the collectors of the transistors 7 and 8 there is no ripple in the constant currents and hence the signal to noise ratio of the circuit employing this constant current circuit is not deteriorated and its operation is stabilized. in addition. as is apparent from FIG. 3, the circuit contains only semiconductive elements and therefore is easily manufacturable as an IC chip.

Referring now more particularly to FIG. 4 a utilization of the constant current circuit of the embodiment of FIG. 3 in an amplifier circuit is illustrated. In FIG. 4 the portion which is enclosed by the dotted line is formed on a single lC chip. An input signal is supplied at an external terminal 18 and is fed to an input terminal 13 of the IC circuit. The base of a PNP transistor 21 is connected to the terminal 13 and its emitter is connected to an external terminal 15 of the IC circuit and to the collector electrode of an NPN transistor 22. The base of the NPN transistor 22 is connected to the collector electrode of the transistor 21. The emitter electrode of the transistor 22 is connected to the base electrode of an NPN transistor 23 whose emitter electrode is connected to an external circuit ground connected to the IC circuit at the terminal 12.

The collector electrode of the transistor 23 is connected to the collector electrode of the transistor 7 and to the base electrode of an NPN transistor 24 whose collector electrode is connected to the external voltage source V,.,. at terminal 1 l. The emitter electrode of the transistor 24 is connected to the collector electrode of the transistor 8 and to an external terminal 14. The remainder of the integrated circuit portion is substantially the same as the embodiment of FIG. 3 and the same reference numerals have been utilized. The external terminal 14 is the output terminal and is connected to a terminal 19 through a capacitor. The terminal 14 is also connected through a resistor 27 to the terminal 15 and to the circuit ground through a resistor 28 in series with a capacitor 29 to supply a negative feedback. A biasing voltage is supplied to the terminal l3 by a voltage divider network 300 and 30b.

The direct coupled transistors 21, 22. 23 and 24 amplify an input signal applied to the terminal 18 so that an amplified output signal appears at the terminal I9. The transistor 23 is in a grounded emitter configuration and the transistor 24 is in a grounded collector (also known as an emitter follower) configuration. The constant current circuit of the embodiment of FIG. 3 is used as the collector load of the transistor 23 and as the emitter load of the transistor 24. A negative feedback is applied to the emitter electrode of the transistor 2l from the terminal 14 through the resistances 27, 28 and the capacitor 29.

Since the collector load of the transistor 23 is the constant current source of the embodiment of FIG. 3. the amplifier circuit in the embodiment of FIG. 4 achieves a very high gain. In prior art circuits of this type where resistors are used as the collector and emitter loads and these resistors are formed on an IC chip. the resistance values cannot be made great and hence high gain can not be achieved. Furthermore in such prior art circuits the currents flowing through these load resistors are relatively large so that the allowable collector losses from the transistors 23 and 24 must also be increased. In contrast. in the circuit of the embodiment of FIG. 4 the collector current of the transis' tor 23 and the emitter current of the transistor 24 can be minimized and hence the allowable collector losses of the transistors 23 and 24 can be minimized. At the same time wasteful current consumption and thermal heating are eliminated.

Still another advantage of the embodiment of FIG. 4 is that since the collector currents of the transistors 7 and 8 are substantially constant as mentioned above. the amplifier circuit can stably achieve a high gain even with respect to variations in the supply voltage V and its signal to noise ratio is not deteriorated by a ripple current in the supply voltage. Still another advantage is that the integrated circuit portion only contains semiconductive elements and only a minimum number of external terminals so that it is easily formed on an IC chip at low cost.

Referring now more particularly to FIG. 5 a modified version of the embodiment of FIG. 3 is depicted. To the extent that the same elements are used from the embodiment of FIG. 3 the same reference numerals have been applied. Emitter resistors 31. 4]. 71 and 81 are placed in series with the emitters of the transistors 3. 4, 7 and 8. respectively. and the transistors 5 and 6 are replaced with separate series connected diode pairs 51 and 52 and 6] and 62. respectively. Thus. the anode of the diode 51 is connected to terminal II and its cathode is connected to the anode of the diode 52. The cathode of the diode 52 is connected to the base electrode of the transistor 3. The anode of the diode 61 is connected to the base of the transistor 4. The cathode of the diode 61 is connected to the anode of the diode 62. The cathode of the diode 62 is connected to the terminal 12. In this embodiment the resistance values of the resistors 71 and SI are varied to change the current from the transistors 7 and 8. The circuit operates in a similar manner to the embodiment of FIG. 3 with the diodes SI. 52 and 6|. 62 supplying a constant base bias voltage to the transistors 3 and 4. respectively.

Referring now more particularly to FIG. 6 a plot illustrating the supply voltage versus output current charac teristics with respect to the conventional constant current circuit shown in FIG. I and the constant current circuit shown in FIG. 5 are illustrated. As is apparent from the figure. as the supply voltage V... is varied the output current I. of the conventional circuit is greatly changed but remains substantially constant in the case of the embodiment of FIG. 5.

In FIG. 7 an amplifier circuit similar to the configuration of FIG. 4 employs the constant current circuit of the embodiment of FIG. 5. The reference numerals of the embodiments of FIGS. 4 and 5 have therefore been used to designate the same elements. An NPN transis tor 25 is connected with its base-emitter junction between the emitter electrode of the transistor 21 and the terminal 15. The collector electrode of the transistor 25 is connected to the terminal II. The base of the transistor 23 is connected to the circuit ground terminal I2 through a resistor 23a. The transistors 21 and 25 thus form a differential input type amplifier and the transistor 7 is again the collector load of the transistor 23 and the transistor 8 is again the emitter load of the transistor 24. The outer or feedback circuit of the em bodiment of FIG. 4 is not shown but may be connected in the same manner to the appropriate terminals. The amplifier embodiment depicted in FIG. 7 has the same desirable attributes as the amplifier circuit of FIG. 4. For example in the amplifier circuit of FIG. 7 a gain without feedback of 76.5dB can be stably obtained.

While in the embodiments depicted with reference to FIGS. 3 and 5 there are provided two transistors 7 and 8 it should be understood by those skilled in the art that in other embodiments only either one of them may be employed or even a plurality of transistors (and emitter resistors) may be similarly connected in parallel. if required. to provide a plurality of constant current sources.

FIG. 8 illustrates one embodiment of a nongrounded constant voltage source formed by utilizing the constant current circuit of the embodiment of FIG. 3. The embodiment of FIG. 3 is modified to have the collector electrode of the transistor 7 connected to an output terminal I5 and the collector electrode of the transistor 8 connected to an output terminal I6. A zener diode 9 and a load 10 are connected in parallel between the terminals I5 and 16. The polarity of the diode 9 is such that a constant voltage is maintained across the terminals IS and I6. It is also to be understood that the base diffusion areas of the transistors 7 and 8 are suitably sc lected to make the respective collector currents I and I equal to each other.

In this arrangement since the current I is equal to the current I the collector current of the transistor 7 flows through the diode 9 and the load 10 to the collector electrode of the transistor 8. Since the transistors 7 and 8 operate as constant current sources their impedances can be taken as infinite so that the equivalent voltage circuit is as shown in FIG. 9. that is. that the terminals I5 and I6 effectively are not connected to the terminal I] and 12. In fact. since a constant voltage is obtained across the diode 9 it becomes the equivalent of a battery 9E as shown in FIG. 10. The battery 9E is therefore not regarded as being grounded. that is the voltage source circuit of the embodiment of FIG. 8 op erates as a non-grounded type constant voltage circuit.

Such a non-grounded type constant voltage circuit is particularly suitable for manufacture as an IC chip since it is constructed only of semiconductive elements. Furthermore. since it is of the non-grounded type. if the load I0 is assumed to be. for example. a negative impedanee transducer an independent coil can be equivalently obtained. that is. a circuit including a coil can be formed on an IC chip.

Referring now more particularly to FIG. it another example of a non-grounded type of constant voltage circuit utilizing the present invention is illustrated. in this embodiment the constant current circuit of the embodiment of FIG. is modified by connecting the collector electrode of the transistor 7 to the terminal 15 and the collector electrode of the transistor 8 to the terminal 16. A load 10 is connected between the terminals and 16. A transistor is connected by its collector electrode to the terminal l5 and by its emitter electrode to the terminal 16. A voltage divider network comprised of two resistors 21 and 22 connected in series between the terminals 15 and 16 provides a base bias voltage to the transistor 20. The emitter resistors 31 41. 7! and 8! are suitably selected to make the currents and equal to each other. The transistor 20 is biased to act as a constant voltage device in the manner of the zener diode 9 in the embodiment of FIG. 8.

In the above-described embodiments only two transistors 7 and 8 are utilized in connection with the transistors 3 and 4, however, in other embodiments a plurality of transistors serving the same functions as the transistors 7 and 8 may be provided with respect to transistors 3 and 4 to provide a plurality of constant voltages or constant current outputs which are independent from one another. The different constant currents. or constant voltages may be produced by suitable design of the base diffusion areas of the transistors 7 and 8 to give different collector currents with the same base bias voltages applied to all of the transistors.

The terms and expressions which have been employed here are used as terms of description and not of limitation. and there is no intention in the use of such terms and expressions of excluding equivalents of the features shown and described. or portions thereof. it being recognized that various modifications are possible within the scope of the invention claimed.

What is claimed is:

l. in combination an amplifier circuit having a constant current circuit as a load therefor, comprising: a first amplifying transistor having an input electrode supplied with a signal to be amplified and an output electrode the first amplifying transistor being con nected in a grounded emitter type configuration; a second amplifying transistor having an output electrode and an input electrode connected to the output elec trode of the first amplifying transistor, the second amplifying transistor being connected in a grounded collector type configuration; a voltage source having at least two output terminals; first and second transistors. the base and collector electrodes of the first transistor being respectively connected to the collector and base electrodes of the second transistor, the respective emitter electrodes of the first and second transistors being connected to separate terminals of the voltage source; third and fourth unidirectional conducting devices for providing biasing voltages between the base and emitter electrodes of each of the first and second transis tors; at least one further transistor, the base and emitter electrodes of said at least one further transistor being connected to the base and emitter electrodes of a corresponding one of the first and second transistors; whereby the collector current of said at least one further transistor with respect to the voltage source is utilizable as a constant current source; and the collector electrode of said at least one further transistor being connected to the output electrode of a corresponding one of the first and second amplifying transistors.

2. The combination of claim 1 and further comprising a second further transistor, the base and emitter electrodes of said second further transistor being connected to the base and emitter electrodes of the outer of said first and second transistors; and the collector electrode of said second further transistor being connected to the output electrode of the other of said first and second amplifying transistors.

3. The combination of claim 2 and further comprising an input amplifying circuit for supplying said signal to be amplified to said first amplifying transistor input electrode; and a feedback circuit for connecting the output electrode of said second amplifying transistor to said input amplifying circuit in negative feedback relation. 

1. In combination an amplifier circuit having a constant current circuit as a load therefor, comprising: a first amplifying transistor having an input electrode supplied with a signal to be amplified and an output electrode, the first amplifying transistor being connected in a grounded emitter type configuration; a second amplifying transistor having an output electrode and an input electrode connected to the output electrode of the first amplifying transistor, the second amplifying transistor being connected in a grounded collector type configuration; a voltage source having at least two output terminals; first and second transistors, the base and collector electrodes of the first transistor being respectively connected to the collector and base electrodes of the second transistor, the respective emitter electrodes of the first and second transistors being connected to separate terminals of the voltage source; third and fourth unidirectional conducting devices for providing biasing voltages between the base and emitter electrodes of each of the first and second transistors; at least one further transistor, the base and emitter electrodes of said at least one further transistor being connected to the base and emitter electrodes of a corresponding one of the first and second transistors; whereby the collector current of said at least one further transistor with respect to the voltage source is utilizable as a constant current source; and the collector electrode of said at least one further transistor being connected to the output electrode of a corresponding one of the first and second amplifying transistors.
 2. The combination of claim 1 and further comprising a second further transistor, the base and emitter electrodes of said second further transistor being connected to the base and emitter electrodes of the outer of said first and second transistors; and the collector electrode of said second further transistor being connected to the output electrode of the other of said first and second amplifying transistors.
 3. The combination of claim 2 and further comprising an input amplifying circuit for supplying said signal to be amplified to said first amplifying transistor input electrode; and a feedback circuit for connecting the output electrode of said second amplifying transistor to said input amplifying circuit in negative feedback relation. 